1. Field of the Disclosure
The present disclosure generally relates to methods and apparatus for characterizing the liquid and solids content of drilling fluids. More particularly, the present disclosure relates to methods and apparatus for characterizing the liquid and solids content of drilling fluids using digital photography. More particularly still, the present disclosure relates to methods and apparatus for d characterizing the liquid and solids content of drilling fluids using fractionation and multi-spectral.
2. Background Art
Wellbore drilling fluids serve many functions throughout the process of drilling for oil and gas. Primary functions include controlling subsurface pressures, transporting to the surface “cuttings” created by the drill bit, and cooling and lubricating the drill bit as it grinds through the earth's crust. Most of the cuttings are removed at the surface by different types of solids-removal equipment, by small bits of formation, such as clays and shales, are invariably incorporated into the drilling fluid as “low-gravity” solids. These low-gravity solids are generally undesirable in that they can contribute to excess viscosity and can adversely impact chemical treatment of the drilling fluid so that it can satisfy other critical functions. The low-gravity solids also are distinguished from high-gravity solids that are added intentionally to increase the density of the drilling fluid.
Fluid density, or mass per unit volume, controls subsurface pressures and contributes to the stability of the borehole by increasing the pressure exerted by the drilling fluid onto the surface of the formation downhole. The column of fluid in the borehole exerts hydrostatic pressure proportional to the true vertical depth of the hole and density of the fluid. Therefore, one can stabilize the borehole and prevent the undesirable inflow of formation fluids by maintaining a proper density of the drilling fluid to ensure that an adequate amount of hydrostatic pressure is maintained.
Several methods of controlling the density of wellbore fluids exist. One method adds dissolved salts such as sodium chloride and calcium chloride in the form of an aqueous brine to drilling fluids. Another method involves adding inert, high specific gravity particulates to drilling fluids to form a suspension of increased density. These inert high-density particulates are often referred to as “weighting agents” and typically include particulate minerals of barite, calcite, or hematite.
While maintaining the density of a drilling fluid is important, other factors also influence the effectiveness of specific drilling fluids in certain drilling operations. Such other factors may include viscosity and composition of the drilling fluid, as well as the fluids ability to cool and lubricate the drill bit. To determine the most effective drilling fluid for a given drilling operation, it is necessary to measure the chemical and physical properties of the drilling fluid as a returns from downhole.
Presently, the standard method for determining the liquid and solids content of the drilling fluid is to conduct a retort analysis. In a retort analysis, a drilling fluid sample is heated at sufficient temperature to vaporize contained liquids, including water, oil, or synthetics. The liquids are condensed, after which the specific volumes can be measured directly in a graduated cylinder. Oil and synthetics have a lower specific gravity than the water and will separate naturally in the measuring container. The total volume of liquids then is subtracted from the starting drilling volume to determine the total solids content. Appropriate mathematical functions are then applied in context of the general composition of the drilling fluid to estimate the fraction of high-gravity and low-gravity solids.
Due to the heating requirements, current retort practices are known to be potentially dangerous, and subject to inaccuracies and inconsistencies. Furthermore, the retort method does not provide means to characterize and differentiate the different solid components beyond the general categorization by gross specific gravity.
Accordingly, there is an existing need for an effective method of characterizing liquid and solid content of drilling fluids.